Progeria is a rare human genetic disease with many features suggestive of premature aging. Previously, cultured progeric fibroblasts have been reported to show abnormalities in growth, DNA repair, tissue factor activity, termolabile proteins, and HLA expression. The proposed work will examine a large number of progeric strains to identify a reliable marker for progeria using a variety of assays. The persistence of an abnormality will be examined to determine under what conditions it is reversible using the technique of cocultivation. This project may lead to information regarding this human genetic disease and the nature of the aging process.